1. Field of the Invention
The present invention relates to a piston coupling mechanism. More specifically, the present invention relates to a piston coupling mechanism, a lockup device for a fluid-type torque transmission device, an elastic coupling mechanism, and a spring installation method for an elastic coupling mechanism.
2. Background Information
One example of a fluid-type torque transmission device is a torque converter, which is a device that serves to transmit torque from an engine to a transmission by means of a fluid contained inside the torque converter. A conventional torque converter chiefly has a front cover, impeller, a fluid chamber, a turbine, and a stator. Torque is delivered from an engine to the front cover. The impeller is fixed to the transmission side of the front cover and forms a fluid chamber. The turbine is arranged to face the engine side of the impeller and is capable of outputting torque to the transmission. The stator is arranged between an inner circumferential part of the impeller and an inner circumferential part of the turbine and is capable of directing the flow of the operating fluid from the turbine toward the impeller. This kind of torque converter is often provided with a lockup device.
The lockup device is arranged in the space between the turbine and the front cover and serves to transmit torque directly from the front cover to the turbine by mechanically coupling the front cover and the turbine together. The lockup device is provided with a circular disc-shaped piston that can engage with and disengage from a friction surface of the front cover by being pressed thereagainst, and an elastic coupling mechanism to transmit torque between the piston and the turbine. A friction coupling part having a friction facing attached thereto is formed on an outer circumferential part of the piston in such a manner as to face the friction surface of the front cover.
Lockup devices having two friction surfaces in order to increase the torque transmission capacity have already been proposed. One such lockup device having two friction surfaces is provided with a clutch mechanism, a piston, and an elastic coupling mechanism. The clutch mechanism has a friction coupling part that can be pressed against a friction surface of the front cover. The piston can push the friction coupling part toward the front cover. The elastic coupling mechanism is fixed to the turbine and serves to couple elastically the turbine and the clutch mechanism together in the rotational direction. Since it is necessary to transmit torque directly from the front cover to the piston when the lockup device is in the locked state, this kind of lockup device is provided with a piston coupling mechanism that couples the piston and the front cover together such that the piston and front cover are non-rotatable and axially moveable relative to each other.
One such piston coupling mechanism involves attaching the piston to the front cover with a plurality of flat springs arranged along a rotational direction. More specifically, one end of each flat spring is fixed with rivets or bolts to a base plate that is fixed by welding or the like to the front cover and the other end of each flat spring is fixed to the piston with rivets or bolts. Thus, the piston can rotate integrally with the front cover and can move axially with respect to the front cover as shown in Japanese Laid-open Patent Publication 10-47453, which is hereby incorporated by reference.
One kind of elastic coupling mechanism provided in a lockup device like that just described is provided with a plurality of coil springs, a first rotary member, a second rotary member, and a third rotary member. The plurality of coil springs is arranged along a rotational direction of the lockup device. The first rotary member is arranged on an axially facing side of the coil springs and serves to support one axially facing side and the radially outward side of the coil springs. The second rotary member is fixed to the first rotary member and supports the rotationally facing ends of the coil springs. The third rotary member supports the rotationally facing ends of the coil springs and is provided in such a manner that it can rotate relative to the first rotary member and second rotary member. The first rotary member is provided with notches or cut-and-raised parts for supporting the rotationally facing ends of the coil springs. When the first rotary member and second rotary member are fixed together, they support the radially inwardly facing side and the other axially facing side of the coil springs.
With this elastic coupling mechanism, the springs are assembled by first arranging the springs using the notches or cut-and-raised parts of the first rotary member and then fixing the second rotary member to the first rotary member.
In a piston coupling mechanism like that just described, the flat springs are fixed to the piston and the front cover using rivets or bolts. Consequently, the piston coupling mechanism has a relatively large number of parts and its assembly requires a large number of man-hours.
Also, in a piston coupling mechanism like that just described, the flat springs are fixed to the front cover through a base plate. Consequently, the weight of the device is relatively high and the number of assembly man-hours is high because of the work required to fix the base plate to the front cover by welding or the like and the work required to fix the return plate to the base plate using rivets, bolts, or other fastening members.
In an elastic coupling mechanism like that just described, since the first rotary member is provided with notches or cut-and-raised parts to support the rotationally facing ends of the coil springs, the shape of the press die used to form the notches or cut-and-raised parts is complex and thus the die cost is relatively high. It is also necessary to increase the rigidity of the rotary member in order prevent the notches or cut-and-raised parts from reducing the rotational strength of the rotary member.
It is also feasible to have a structure in which the second rotary member is arranged on a first rotary member that does not have notches or cut-and-raised parts in such a manner as to form spaces for the springs. The springs are then arranged in the spaces and a separate member is fixed to the first and second rotary members to support the radially inward facing side and the other axially facing side of the springs. However, the problem with this kind of structure is that a new separate member is required to support the radially inward facing side and the other axially facing side of the springs.
In view of the above, there exists a need for a piston coupling mechanism, lockup device for a fluid-type torque transmission device, elastic coupling mechanism, and spring installation method for an elastic coupling mechanism that overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.